Optical diffraction of electron micrographs of negatively-stained neurotubules and ciliary or flagellar outer-fiber microtubule doublets will be used to determine basic parameters of tubulin dimer and subunit lattices. X-ray diffraction of oriented gels of neurotubules polymerized in vitro and also of ciliary or flagellar outer-fiber doublet and A-singlet microtubules will be used to determine the shape and position of tubulin subunits within the basic surface lattice. The purpose of this work is to define the three-dimensional arrangement of tubulin molecules in the wall of various microtubules and to determine how this arrangement might confer specificity of binding by accessory protein to certain microtubules in cilia and flagella. Elucidation of the substructure of microtubules is vital to the understanding of microtubule function, at a molecular level in nerve maintenance and growth secretion, ciliary and flagellar motion, and chromosome movement via spindle fibers. BIBLIOGRAPHIC REFERENCES: Stephens, R.E. and K.T. Edds (1976). "Microtubules: Structure, Chemistry, and Function," Physiological Reviews (in press). Cohen, C., D. DeRosier, S.C. Harrison, R.E. Stephens, and J. Thomas (1975). "X-Ray Patterns from Microtubules," Ann. N.Y. Acad. Sci. 235: 53-59.